H2O2 + KI + H2S2O3 = H2O + I2 + K2S4O6O4

H_2O_2 hydrogen peroxide + KI potassium iodide + H2S2O3 ⟶ H_2O water + I_2 iodine + K2S4O6O4

Balance the chemical equation algebraically: H_2O_2 + KI + H2S2O3 ⟶ H_2O + I_2 + K2S4O6O4 Add stoichiometric coefficients, c_i, to the reactants and products: c_1 H_2O_2 + c_2 KI + c_3 H2S2O3 ⟶ c_4 H_2O + c_5 I_2 + c_6 K2S4O6O4 Set the number of atoms in the reactants equal to the number of atoms in the products for H, O, I, K and S: H: | 2 c_1 + 2 c_3 = 2 c_4 O: | 2 c_1 + 3 c_3 = c_4 + 10 c_6 I: | c_2 = 2 c_5 K: | c_2 = 2 c_6 S: | 2 c_3 = 4 c_6 Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c_5 = 1 and solve the system of equations for the remaining coefficients: c_1 = 6 c_2 = 2 c_3 = 2 c_4 = 8 c_5 = 1 c_6 = 1 Substitute the coefficients into the chemical reaction to obtain the balanced equation: Answer: | | 6 H_2O_2 + 2 KI + 2 H2S2O3 ⟶ 8 H_2O + I_2 + K2S4O6O4

+ + H2S2O3 ⟶ + + K2S4O6O4

hydrogen peroxide + potassium iodide + H2S2O3 ⟶ water + iodine + K2S4O6O4

Construct the equilibrium constant, K, expression for: H_2O_2 + KI + H2S2O3 ⟶ H_2O + I_2 + K2S4O6O4 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the activity expression for each chemical species. • Use the activity expressions to build the equilibrium constant expression. Write the balanced chemical equation: 6 H_2O_2 + 2 KI + 2 H2S2O3 ⟶ 8 H_2O + I_2 + K2S4O6O4 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i H_2O_2 | 6 | -6 KI | 2 | -2 H2S2O3 | 2 | -2 H_2O | 8 | 8 I_2 | 1 | 1 K2S4O6O4 | 1 | 1 Assemble the activity expressions accounting for the state of matter and ν_i: chemical species | c_i | ν_i | activity expression H_2O_2 | 6 | -6 | ([H2O2])^(-6) KI | 2 | -2 | ([KI])^(-2) H2S2O3 | 2 | -2 | ([H2S2O3])^(-2) H_2O | 8 | 8 | ([H2O])^8 I_2 | 1 | 1 | [I2] K2S4O6O4 | 1 | 1 | [K2S4O6O4] The equilibrium constant symbol in the concentration basis is: K_c Mulitply the activity expressions to arrive at the K_c expression: Answer: | | K_c = ([H2O2])^(-6) ([KI])^(-2) ([H2S2O3])^(-2) ([H2O])^8 [I2] [K2S4O6O4] = (([H2O])^8 [I2] [K2S4O6O4])/(([H2O2])^6 ([KI])^2 ([H2S2O3])^2)

Construct the rate of reaction expression for: H_2O_2 + KI + H2S2O3 ⟶ H_2O + I_2 + K2S4O6O4 Plan: • Balance the chemical equation. • Determine the stoichiometric numbers. • Assemble the rate term for each chemical species. • Write the rate of reaction expression. Write the balanced chemical equation: 6 H_2O_2 + 2 KI + 2 H2S2O3 ⟶ 8 H_2O + I_2 + K2S4O6O4 Assign stoichiometric numbers, ν_i, using the stoichiometric coefficients, c_i, from the balanced chemical equation in the following manner: ν_i = -c_i for reactants and ν_i = c_i for products: chemical species | c_i | ν_i H_2O_2 | 6 | -6 KI | 2 | -2 H2S2O3 | 2 | -2 H_2O | 8 | 8 I_2 | 1 | 1 K2S4O6O4 | 1 | 1 The rate term for each chemical species, B_i, is 1/ν_i(Δ[B_i])/(Δt) where [B_i] is the amount concentration and t is time: chemical species | c_i | ν_i | rate term H_2O_2 | 6 | -6 | -1/6 (Δ[H2O2])/(Δt) KI | 2 | -2 | -1/2 (Δ[KI])/(Δt) H2S2O3 | 2 | -2 | -1/2 (Δ[H2S2O3])/(Δt) H_2O | 8 | 8 | 1/8 (Δ[H2O])/(Δt) I_2 | 1 | 1 | (Δ[I2])/(Δt) K2S4O6O4 | 1 | 1 | (Δ[K2S4O6O4])/(Δt) (for infinitesimal rate of change, replace Δ with d) Set the rate terms equal to each other to arrive at the rate expression: Answer: | | rate = -1/6 (Δ[H2O2])/(Δt) = -1/2 (Δ[KI])/(Δt) = -1/2 (Δ[H2S2O3])/(Δt) = 1/8 (Δ[H2O])/(Δt) = (Δ[I2])/(Δt) = (Δ[K2S4O6O4])/(Δt) (assuming constant volume and no accumulation of intermediates or side products)

| hydrogen peroxide | potassium iodide | H2S2O3 | water | iodine | K2S4O6O4 formula | H_2O_2 | KI | H2S2O3 | H_2O | I_2 | K2S4O6O4 Hill formula | H_2O_2 | IK | H2O3S2 | H_2O | I_2 | K2O10S4 name | hydrogen peroxide | potassium iodide | | water | iodine | IUPAC name | hydrogen peroxide | potassium iodide | | water | molecular iodine |

| hydrogen peroxide | potassium iodide | H2S2O3 | water | iodine | K2S4O6O4 molar mass | 34.014 g/mol | 166.0028 g/mol | 114.1 g/mol | 18.015 g/mol | 253.80894 g/mol | 366.4 g/mol phase | liquid (at STP) | solid (at STP) | | liquid (at STP) | solid (at STP) | melting point | -0.43 °C | 681 °C | | 0 °C | 113 °C | boiling point | 150.2 °C | 1330 °C | | 99.9839 °C | 184 °C | density | 1.44 g/cm^3 | 3.123 g/cm^3 | | 1 g/cm^3 | 4.94 g/cm^3 | solubility in water | miscible | | | | | surface tension | 0.0804 N/m | | | 0.0728 N/m | | dynamic viscosity | 0.001249 Pa s (at 20 °C) | 0.0010227 Pa s (at 732.9 °C) | | 8.9×10^-4 Pa s (at 25 °C) | 0.00227 Pa s (at 116 °C) | odor | | | | odorless | |